Patent GB-626756-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: B21B37/54
Filed: 1947-03-17
Abstract: 626.756. Control of two D.C. motors. GENERAL ELECTRIC CO., Ltd., and FRIEDLANDER, E. S. March 17, 1947, No. 7323. [Class 38(iii)] An electric motor control system for a cold strip rolling mill of the kind comprising an electric motor 11 adapted to drive the last roll stand and an electric motor 1 adapted to drive means for reeling strip is provided with tachometer generators 12 and 13 which are respectively associated with and adapted to measure the speed of the last roll stand and of the strip reeling means, and further means are provided for measuring the ratio of the output voltages of the tachometer generators, the said further means, being arranged to give an indication of, or to effect a control in dependence upon, the reel radius. The reel motor 1 is supplied from a constant-speed generator 2 and has a field winding 3 supplied from mains 4. A generator field winding 5 is energized from an A.C. source through a transformer 6 and a grid-controlled mercury arc rectifier 7. The difference of the output voltage of the generator 12 and that across a portion of a potentiometer 14, which is fed from the generator 12 and that across a portion 18 through an amplifier 16. The motor 18 adjusts the position of a tapping 15 of the potentiometer 14 so as to maintain the resultant voltage input to the amplifier 16 at zero value. The position of the tapping 15 affords an indication of the ratio of the voltages of the generators 12 and 13, and as the diameter of the reel increases and the speed of the motor 1 decreases, the pilot motor 18 adjusts the position of a tapping 22 of a resistor 23, which is connected in series with the field winding 3, so as to increase the field excitation and torque of the reel motor. In order to provide constant strip tension despite changes in the speed of the strip and variations of the inertia of the reel, the value of the reel motor armature current is adjusted by means of a valve amplifier 24 which is associated with the grid circuit of the rectifier 7, the input-voltage to this amplifier haviing components compensating for such changes. A tapping 31 of a resistor 28 provides for tension control of the strip, a resistor 10 providing a feed-back signal voltage proportional to the armature current of the motor 1. A tapping 27 on a potentiometer 26, the position of which is dependent upon the reel radius and its inertia, is moved with the tapping 15 and is arranged to coincide with a fixed tapping 35 when the kinetic energy of the system is at a minimum. A tachometer generator 38 is associated with a motor driving the master controller and provides a signal voltage which is dependent upon the intended rate of acceleration of the mill, a delay reactor 39 being provided. Tappings 33, 40, and 37 provide means for adjusting the values of the various voltage-components supplied to the amplifier 24. A resistance-capacity stabilizer may be placed on the input side of the amplifier 24. A valve amplifier may amplify the voltagedrop across the resistor 10. The generator 12 may replace the generator 38 in the supply circuit to the amplifier 24.